The present invention relates to a dental implant system.
Dental implants are embedded in the jaw bone and serve to anchor one or more artificial teeth or dentures. Most implant systems involve a relatively long implant cylinder which is placed into a custom bored hole in the jawbone, then left for several months to allow healing and bone integration. Then the implant must be exposed for attachment of a dental prosthetic appliance such as a crown, denture, partial denture or bridge. This generally involves the dentist cutting out a flap of tissue which is peeled back to expose the implant, and secured by sutures after installing the prosthesis. This results in a relatively large area of trauma with a certain degree of pain to the patient and risk of post-operative infection.
Another problem with conventional implants is their length, which makes them difficult to implant in the distal jaw region, where there is insufficient depth to enable their insertion without interference with the mandibular nerve, without the assistance of a dental surgeon to locate the precise position of the nerve and ensure that the implant does not interfere with it. A shorter cylindrical implant would not normally be suitable since it would provide insufficient xe2x80x9choldxe2x80x9d and would likely become loosened with time if anchored to a denture or bridge. Also, side to side forces on the implant lead to bone erosion and trauma. Thus, dentures or bridges are often not anchored at the rear of the jaw. However, this has the disadvantage that trauma to the tissue and underlying bone beneath the denture occurs as a result of the denture repeatedly impacting the bone, particularly with long dentures which will tend to tilt or rotate about their attachment or anchor points during chewing or other jaw motions. This biting pressure can result in bone erosion or resorption down to the level of the nerve.
It is an object of this invention to provide an improved dental implant system and method which is less likely to cause significant tissue trauma and which reduces bone erosion as a result of denture wear.
It is a further object of this invention to provide an improved system and method for exposing an implant site after osseointegration has taken place.
According to a first aspect of the present invention, a dental implant assembly is provided which comprises a first, implant member for implanting in the distal region of the jaw bone, and a second member or rest factor for attachment to the implant member. The two members have cooperating releasable securing devices for releasably securing them together, preferably comprising a screw threaded bore in the implant member and a corresponding threaded portion on the rest factor member. The rest factor member projects up to just above the level of the tissue overlying the jaw bone and has an upper surface opposing an overlying portion of a prosthesis anchored elsewhere in the jaw to form a rest for the prosthesis which accepts down pressure only, and which acts as a support to prevent or restrict bone erosion. The implant member has a selected height less than the depth of the mandibular nerve at the implant site, so that it can be embedded in the bone without risk of interference with the nerve. At the same time, the implant member is as wide as possible, and preferably has the maximum diameter possible according to the width of the patient""s alveolar ridge at the implant site. The implant member diameter is preferably selected to be 1 mm less than the available alveolar ridge or bone width at the implant site. Implant members in a range of different heights and diameters are preferably provided to meet the requirements of a range of patients. Preferably, implant members with heights of 2 mm, 4.5 mm, 7 mm and 10 mm are provided, to allow for patients whose jawbone is already eroded to some extent. Implant members with diameters ranging from about 4 mm to 6 mm may be provided.
Since the implant member is of relatively large diameter, it has a relatively large surface area resisting downward forces. In a preferred embodiment of the invention, the implant member has a generally cylindrical body with an upper end portion and downwardly depending stem portion which engages in a corresponding recess drilled out in the bone. Preferably, at least part of the stem portion at the lower end of the implant member has an annular recess forming an outer rim and central boss. This engages a corresponding annular recess drilled out in the bone to resist sideways movement of the implant. This will resist sideways movement of the implant during osseointegration, and also provides additional depth for securing the rest factor to the implant member. A bore of corresponding shape to the undersurface of the implant member is drilled out in the jawbone at the implant site, so that when the implant member is positioned in the bore, the peripheral rim will provide stabilization of the member against lateral movement during the osseointegration period. The shape of the undersurface of the implant provides a large area of bone to implant contact for osseointegration, and significant resistance to both lateral and downward forces both during and after the osseointegration period. Preferably, at least two separate or double lead threads are provided, and triple or quadruple threads may be provided for added retention. Bone grows into the gaps between threads.
The outer surface of the stem portion of the implant preferably has threads to provide additional surface area for bone attachment. Bone grows into the area above and below the threads to resist loosening of the implant.
Since the rest factor is not anchored to the prosthesis, the risk of jaw bone erosion or damage as a result of upward forces is reduced. However, the rest factor does accept down pressure as a result of biting pressure of the denture, and will thus reduce the risk of trauma to the tissue and jawbone erosion as a result of pressure. The localized contact between the rest factor and the underlying bone via the implant member reduces or substantially eliminates pressure trauma on the entire bone.
If desired, the upper surface of the rest factor and the opposing portion of the prosthesis may be provided with opposing, non-retentive mating formations, such as opposing slightly convex and concave formations, for guiding the prosthesis against the rest factor. However, these formations do not provide any upwards retention of the prosthesis. A series of such rest factors may be provided at appropriate locations in the jaw where maximum down pressure from a denture is encountered, considerably reducing the discomfort of denture use and reducing the risk of tissue and jawbone damage as would result from conventionally anchored dentures.
The rest factor may be preformed with a suitable rest surface in incremental heights, in which case the procedure after removing the healing screw comprises selecting an appropriate height rest factor and securing the selected rest factor in the implant member.
The implant member may be relatively short with a relatively large diameter, so that it can be anchored securely in the jawbone without needing a deep bore to be drilled out. The implant member is provided in several heights. The shortest of the implants will be shorter and wider than conventional cylindrical implants, and thus can be used at the back or posterior mandible of the jaw where the nerve position prevents or restricts the use of long implants. This implant is particularly suitable for positioning a rest factor in the second molar area in conjunction with implant dentistry where cantilevered bridges or anterior implants need support or in other places where a rest factor is needed in dentistry. The implant requires less bone to be drilled out than conventional cylindrical implants, reducing or minimizing bone loss, and is able to accept hundreds of pounds of down pressure from an overlying denture or prosthesis.
After bone integration, the implant can be recovered by piercing the tissue overlying a healing screw secured to the implant with a pointed end of a locating guide tool, probing the implant site with the pointed end until it engages a hole in the top of the healing screw, inserting the pointed end into the hole, utilizing a tissue punch centered on the guide tool to cut out a plug of tissue directly over the implant, and subsequently removing the healing screw.
Thus, the locating tool and tissue punch can be removed together from the implant site, carrying with them the tissue plug to expose the healing screw for removal with a separate tool. The implant is then exposed for secondary healing or restoration procedures while a minimum amount of tissue has been disturbed and little or no suturing is required. This considerably reduces the trauma, secondary tissue healing, discomfort to the patient, and risk of infection.
The implant member provides osseointegration with good resistance to loosening forces as a result of chewing. It may alternatively be used to secure other dental devices such as an implant denture anchor or an implant magnet abutment.
An implant locating and exposing tool may be used to recover the implant. The tool comprises an elongate shaft having a head at one end and a locating probe at the opposite end having a sharp end for probing the tissue over an implant site to locate a central hole in the top of a healing screw, and a cutter member mounted on the elongate member with its cutting face facing in the same direction as the locating probe, the cutter member being movable along the elongate shaft to cut out a plug of tissue overlying a healing screw.
Thus, the healing screw can be located and the overlying tissue removed in one step, without having to cut out a relatively large flap of tissue.
The healing screw may be provided with a concave upper surface so that the locating probe will be guided towards the central opening.
The implant system and method described above provides a rest surface for an overlying cantilevered bridge or denture which is anchored elsewhere in the jaw, on which the denture can rest and which accepts down pressure from the denture, reducing tissue trauma. Rest surfaces may be provided wherever needed, in conjunction with the conventional implants and anchors used for securing the denture or prosthesis in the jaw. The improved implant recovery tool and method produces minimal trauma when exposing a previously embedded implant for subsequent connection to either a rest factor or to a conventional anchor or magnet abutment.